1. Technical Field of the Invention
The present invention relates to brushless AC (alternating-current) motors installed on automobiles and trucks, for example, and relates to control apparatuses for the brushless AC motors.
2. Related Art
Three-phase AC motors are widely used. FIG. 43 is a schematic vertical cross-sectional view illustrating an example of the configuration of such a three-phase brushless AC motor as a surface magnet brushless motor. In the figure, indicated by 511 is a motor output shaft, by 512 is a rotor core, by 519 are N- and S-pole permanent magnet segments attached to the surface of the rotor, by 513 is a bearing, by 514 is a stator core, by 515 is a coil end formed of the windings and by 516 is a motor case.
FIG. 44 is a horizontal cross-sectional view taken along a line AA-AA of FIG. 43. This three-phase AC motor has four poles and six slots and is provided with short-pitch concentrated winding.
Indicated by TBU1 and TBU2 are U-phase stator poles, by TBV1 and TBV2 are V-phase stator poles and by TBW1 and TBW2 are W-phase stator poles.
Stator poles of each of the phases are provided with turns of windings. Indicated by WBU1 and WBU2 are U-phase windings, by WBV1 and WBV2 are V-phase windings and by WBW1 and WBW2 are W-phase windings. Indicated by 517 are N-pole permanent magnet segments and by 518 are S-pole permanent magnet segments.
In the motor shown in FIGS. 43 and 44, the rotor can be rotated by controlling the attraction force and the repulsive force acting between the stator poles and the S- and N-pole magnet segments 517 and 518 magnet, with the control of the current passing through the phase windings.
FIG. 45 is a winding diagram in which the abscissa indicates position θer, in terms of electrical angle, of the stator in the rotating direction. Since this motor is exemplified as a motor having four poles, the electrical angle indicated in the abscissa ranges from 0° to 720°. Indicated by U is a terminal of the U-phase, to which U-phase current Iu is applied, by V is a terminal of the V-phase, to which V-phase current Iv is applied, and by W is a terminal of the W-phase, to which W-phase current Iw is applied. Indicated by N is a neutral point of the three-phase Y connection.
Surface magnet brushless motors as shown in FIGS. 43 to 45 have been widely used as excellent motors. However, as shown in FIGS. 44 and 45, the windings are separately wound about the stator poles, i.e. teeth, of the individual phases. Although such a brushless motor has a relatively simple structure, further simplification may be expected.
An example of such a brushless motor can be seen in Japanese Patent Application Laid-Open Publication No. 6-261513 (see FIGS. 1 and 4).
It should be appreciated that, throughout the specification, when a term “circumferential direction” or “circumferentially” is used, the term indicates the direction along the circumference of the motor. Also, when a term “axial direction” or “axially” is used, the term indicates the direction along the shaft of the rotor.
FIG. 46 is a vertical cross-sectional view illustrating an example of another brushless AC motor. This motor is a three-phase eight-pole motor. In the figure, indicated by 541 is a rotor shaft, by 542 is a permanent magnet assembly of the rotor, by 543 is a motor case and by 544 is a back yoke portion of the stator core. Further, indicated by 549 are U-phase stator poles, by 54A are V-phase stator poles and by 54B are W-phase stator poles. Indicated by 545 is a negative U-phase winding wound into a looped shape (i.e., ring-shaped) substantially along the circumference. Indicated by 546 is a positive V-phase winding and by 547 is a negative V-phase winding, each also having a looped shape. Indicated by 548 is a positive W-phase winding.
It should be appreciated that a negative winding is a winding which is wound in a direction opposite to the winding direction of a positive winding. In other words, a negative winding is a winding through which electrical current is passed in a direction reverse of the direction of the electrical current passed through a positive winding.
FIG. 47 is a linear development showing a relationship between the shapes of the stator poles of the individual phases of the motor shown in FIG. 46, as seen from the rotor, and the respective windings. Specifically, indicated by 549 are the shapes of the U-phase stator poles arranged along the circumferential direction as seen from the rotor. The horizontal direction as viewed in the figure corresponds to the circumferential direction. As can be seen, four U-phase stator poles 549 are arranged along one circuit of the motor. Likewise, indicated by 54A are V-phase stator poles and by 54B are W-phase stator poles.
The U-, V- and W-phase stator poles 549, 54A and 54B are relatively and mutually shifted by 120° in electrical angle, i.e. 30° in mechanical angle, in the circumferential direction. The vertical direction as viewed in FIG. 47 corresponds to the axial direction. FIG. 47 exemplifies the stator poles of the individual phases, which are mutually shifted between phases in the axial direction.
In order to generate rotation torque based on the principle of operation of the brushless motor shown in FIGS. 43 to 45 in the arrangement of the stator poles as shown in FIG. 47, turns of the windings as indicated by the solid and broken lines in FIG. 47 may be given, with the supply of three-phase current.
First, the U-phase winding is routed along a path (1) and wound about the leftmost U-phase stator pole by a predetermined number of turns Nn. Then, the U-phase winding is routed along a crossover path (2) and wound about the second U-phase stator pole from the left along paths (3), (4), (5) and (6) by the predetermined number of turns Nn. After that, the U-phase winding is routed along a crossover path (7) and wound about the third U-phase stator pole from the left along paths (8), (9) and (10) by the predetermined number of turns Nn. Finally, the U-phase winding is wound about the fourth U-phase stator pole from the left in the similar manner and connected to the neutral point N of the three-phase star connection.
For the V phase, the turns of the winding is imparted in the similar manner. Specifically, the V-phase winding is routed along a path (11) and wound about the leftmost V-phase stator pole by the predetermined number of turns Nn. Then, the V-phase winding is routed along a crossover path (12) and wound about the second V-phase stator pole from the left along paths (13), (14), (15) and (16) by the predetermined number of turns Nn. After that, the V-phase winding is routed along a crossover path (17) and wound about the third V-phase stator pole from the left along paths (18), (19) and (20) by the predetermined number of turns Nn. Finally, the V-phase winding is wound about the fourth V-phase stator pole from the left in the similar manner and connected to the neutral point N of the three-phase star connection.
For the phase W, the turns of the winding is imparted in the similar manner. Specifically, the W-phase winding is routed along a path (21) and wound about the leftmost W-phase stator pole by the predetermined number of turns Nn. Then, the W-phase winding is routed along a crossover path (22) and wound about the second W-phase stator pole from the left along paths (23), (24), (25) and (26) by the predetermined number of times Nn. After that, the W-phase winding is routed along a crossover path (27) and wound about the third W-phase stator pole from the left along paths (28), (29) and (30) by the predetermined number of turns Nn. Finally, the W-phase winding is wound about the fourth W-phase stator pole from the left in the similar manner and connected to the neutral point N of the three-phase star connection.
Let us assume that, in such a configuration shown in FIG. 47, the number of turns Nn is the same as in the motor shown in FIG. 45, and the phases of the stator poles of the individual phases coincide, in the circumferential direction, with those of the permanent magnet segments of the rotor. In this case, the electromagnetic force associated with the generation of the circumferential torque and acting between the stator poles and the permanent magnet segments of the rotor will be the same between the motor configurations shown in FIGS. 45 and 47.
Hereinafter will be discussed, in detail, the electromagnetic action of the current passing through the windings shown in FIG. 47. As can be seen in FIG. 47, in the phase U, the same current passes in the opposite directions through the paths (1) and (3) to thereby cancel field intensity H generated by the current passing through these paths. Accordingly, no electromagnetic action is caused, negating the need of supplying current through either of the paths. The same applies to the paths (5) and (8).
A magnetic path to the back yoke connected to each of the stator poles of the three phases is configured as shown in FIG. 47. Since the paths (6) and (10) are located outside the magnetic path, the field intensity H caused by the current passing through the paths (6) and (10) will act on a magnetic circuit serially connected to an air portion that surrounds the winding portions associated with these paths. Accordingly, since the magnetic resistance of such an air portion is very large, the current passing through the paths (6) and (10) will barely act on the magnetic circuit of the motor, negating the need of the winding portions associated with these paths and the current passing therethrough. Thus, the winding portions associated with the paths (6) and (10) or the like and located outside the core can be omitted.
Let us discuss the phase V. As can be seen in FIG. 47, the same current passes in the opposite directions through the paths (11) and (13) to thereby cancel the field intensity H generated by the current passing through the paths (11) and (13). Accordingly, no electromagnetic action is caused, negating the need of supplying current through either of the paths. The same applies to the paths (15) and (18). Four paths, i.e. the paths (16) and (20) as well as the paths (14) and (19), unlike the case of the phase U, are located inside the stator core to permit magnetomotive force to act on the stator poles. Therefore, these four paths cannot be omitted.
Let us discuss the phase W. As can be seen in FIG. 47, the same current passes in the opposite directions through the paths (21) and (23) to thereby cancel the field intensity H generated by the current passing through the paths (21) and (23). Accordingly, no electromagnetic action is caused, negating the need of supplying current through either of the paths. The same applies to the paths (25) and (28). Similar to the paths (4) and (9) of the phase U, the paths (26) and (30) are located inside the stator core to permit magnetomotive force to act on the stator poles. Therefore, these paths cannot be omitted. The winding portions corresponding to the paths (24) and (29) can be omitted, because they are located outside the core, similar to the paths (6) and (10) of the phase U.
As described above, the windings portions located between the stator poles in the circumferential direction can be omitted. Therefore, the windings shown in FIG. 47 can be replaced by six loop windings wound in the circumferential direction. In this case, two loop windings that will be located at both ends in the axial direction can be omitted because they are located outside the magnetic circuit of the stator and thus will barely influence the electromagnetic action within the stator. As a result, four loop windings can be provided as the loop windings 545, 546, 547 and 548 shown in FIG. 46. FIG. 49 illustrates a configuration of these windings in the state of being linearly developed. In the figure, the abscissa indicates mechanical angle and the broken lines indicate the image of the permanent magnet assembly 542 facing the stator.
FIG. 50 illustrates in a simplified fashion the windings shown in FIG. 49. The windings 545 and 546, which are arranged in the same space, can be combined into a single loop winding 571 shown in FIG. 50. The current (−Iu) that should be passed through the winding 545 and the current (Iv) that should be passed through the winding 546 may be arithmetically added up and passed through the winding 571 as current Im.Im=(−Iu+Iv)  (1)
Similarly, the windings 547 and 548, which are arranged in the same space, can be combined into a single loop winding 572 shown in FIG. 50. The current (−Iv) that should be passed through the winding 547 and the current (Iw) that should be passed through the winding 548 may be arithmetically added up and passed through the winding 572 as current In.In=(−Iv+Iw)  (2)
In this way, the windings are simplified and thus the manufacture of motors can be facilitated. Also, Joule loss can be reduced by 25% and thus the motor efficiency can be enhanced.
The vertical cross section of the motor shown in FIG. 46 may be turned to the vertical cross section of the motor, as shown in FIG. 51, having simplified windings 571 and 572. A loop winding may have a specific shape as shown in FIGS. 48A and 48B, taking the loop winding 545 of FIG. 46 as an example. FIG. 48A is a plan view of the loop winding and FIG. 48B is a right-side view of the loop winding. Since the structure is simple, loop windings, as shown in FIGS. 48A and 48B, can be easily manufactured when compared with the conventional windings which were wound about the teeth concerned.
FIG. 52 exemplifies the voltages, currents and connecting method for the windings illustrated in FIGS. 50 and 51. FIG. 52 shows the configuration of a three-phase delta connection in the absence of one winding line. Currents to be supplied to motor terminals 591, 592 and 593 are expressed by Im=−Iu+Iv, Io=−Iw+Iu and In=−Iv+Iw, respectively, that constitute balanced three-phase currents.Io=−Iw+Iu=−Im−In  (3)
The voltages, excepting those corresponding to impedance drop of the windings, constitute balanced three-phase voltages. In the case of a compact motor, however, the proportion of the voltages corresponding to the impedance drop in the motor voltages may become large, which may lead to the problem of unbalanced voltages. Reference may be made to Japanese Patent No. 4007339 (see FIGS. 1, 11 and 13).